Apparatus for radio direction finding



Jan. 8, 194n J. R. STEINHOFF APPARATUS FOR RADIO DIRECTION FINDING FiledNov. 4, 1941 2 Sheets-Sheet l Jan.- s, 1946. l J. R. STEINHOFF 2,392,420

APPARATUS FOR RADIO DIRECTION FINDING Filed Nov. 4, 1941 2 Sheets-Sheet2 v da@ sfmzfwff Patented Jan. 8, 1946 UNITED STATES TT OFFICE APPARATUSFOR `RAlDIO DIRECTION FINDING 12 Claims.

This invention relates to improvements in apparatus for radiodirectional finding and more particularly to apparatus for indicating byradio the direction of movement of a vehicle.

An object of the invention is to provide a re' liable and efficientapparatus for providing visual indication of the direction of apredetermined transmitter with respect to a moving vehicle.

Another object of the invention is to provide for radio directionfinding, a dynamometer type of instrument capable of rotating throughthree hundred sixty degrees.

Another object of the invention is to provide an instrument design whichwill enable the convenient utilization in the dynamometer type, ofadjustable coils for compensating errors caused by absorption orreradiation of the signal by objects in the vicinity.

Another object of the invention is to provide an improved system fordetermining the direction of a radio transmitter including non-rotatingantennae, a radio receiver, two sets of rotary contacts and aninstrument which will be responsive to four series of interspersedsignals amplified and rectified separately by the receiver, includingprovision for four separate D. C. potentials proportional to the seriesof impulses.

The above and other objects of the invention will be clearly understoodby referring to the following detailed description and the accompanyingdrawings forming a part thereof, wherein Figure 1 shows a wiring diagramembodying the system;

Figure 2 is a plan view of the dynamometer type of instrument;

Figure 3 is a perspective fragmentary view of `associated stationary andmoving coils forming a part of said instrument;

Figure 4 is a detailed View of one of the pairs of bearings utilized insaid instrument;

Figure 5 is a detailed view in perspective showing a bracket formounting one of the compensating coils; and

Figure 6 is a detailed section on an enlarged scale of a portion of theinstrument showing the coil bracket slidably disposed therein.

In the art of directional radio receivers, it has been a practice insome instances to alternate the connections of a directional loopantenna, which is inductively coupled to a vertical antenna and theinput of a radio receiver, to provide two series of signal voltagesproportional to the phase relation to the vertical. When the plane ofthe loop is in line with the transmitter and in phase with the verticalantenna, a maximum signal is CIL applied to the receiver. Rotating theloop decreases the signal and the minimum is obtained when the loop isone hundred eighty degrees from maximum position. However, automaticcompasses of the type utilized heretofore have not been reliable alwayswith respect to fine accuracy and reliability, and in addition haverequired considerable apparatus to the end that a more accurate,reliable and lightweight apparatus is essential.

In the present invention two loops are utilized, the connections offirst one loop and then the other being reversed by rotating the switchto provide four series of signal voltages to the receiver. These fourinterspersed series or signals are amplified and rectied separately bythe receiver and further amplified by the voltage ampliner. A secondrotating switch mechanically coupled to the first switch interrupts theoutput of the voltage amplifier and provides four separate D. C.potentials proportional to the four series of signal impulses applied tothe receiver. Said four potentials are connected to stationary coils inthe instrument as well as to condensers which retain the applied voltageto the coils in the same respect that a lter mechanism retains itscharge in a half wave rectier circuit.

Referring to the drawings wherein similar parts are indicated byidentical reference numerals, the illustrated method described aboveincludes vertical antenna A, a radio receiver C which may be of anyknown design, two sets DI and D2 of rotary contacts, a voltage amplier Eand an indicating instrument which comprises an important aspect of thepresent invention and which will be described in detail hereinafter. Theelectrical connections of this system are clearly shown in Figure 1. Thefixed loop antennae BI and B2 are center tapped and are of aconventional design, loop Bl being mounted parallel to the fore and aftaxis of the craft and loop B2 being fixed at ninety degrees to suchaxis, a rotating switch Gl reverses the connections of flrst loop Bl andthen loop B2 as shown in Figure 1, providing four series of signalvoltages to the receiver C. These four interspersed series of signalsare amplified and rectified separately by the receiver and furtheramplified by the voltage ampliiier E. The rotary switch G2 which ismechanically coupled to rotary switch Gl by shaft T, interrupts theoutput of the voltage amplifier and provides four separate D. C.potentials proportional to the four series of signal impulses applied tothe receiver.

The four D. C. potentials are connected to the two stationary coils HI,H2 in the indicator as shown in Fi-g. 1, also to condensers KI, K2, K3and K4 lwhich retain the applied voltage to the coils in the samerespect that a lter condenser retainsits charge in a half wave rectifiercircuit.

An essential element in the present invention is the instrument F whichis a meter of the moving coil type and is similar to a dynamometer inconstruction. A moving coil L is wound on an aluminum frame LI so as torotate within two stationary coils HI and H2, its movement being tencoils #2", according to the signal applied to the receiver. A variableresistor #26 is adjustedl to zero potential across the coils with zerosignal across the receiver input; as the signal increases,

current, therefore increasing the voltage across governed by magneticenergies only, no springs being used therein. Two pivots L3 and L4 areattached to the moving coil as is shown in Figure 3, and a pointer M isfixed to the top pivot L3 to extend at right angles to the moving coilL. Pivots L3 and L4 rotate freely in adjusting screws N, upper andlower, as shown in Fig. 4, such adjusting screws being similar to thoseused inmany types of electrical indicating devices. Each adjusting screwis recessed with two communicating areas NI and N2, N I fixedlyreceiving a bored jewel O which oiers a minimum of friction to thepivots. To establish positive electrical contact to the pivots, whichare connected to the coil L, a small hole OI is cut in the center of thejewel. Recess portion N2 beneath the jewel is a small well containingmercury P for maintaining electrical contact with a ne wire Q ofplatinum or other conductive material attached to the tip of the pivotas is shown in Fig. 4;

When the pivots are inserted in the adjusting screws, the platinum wireextends through the hole in the jewel into .the mercury lled well. Thepivot resting in the jewel cavity prevents the mercury from escaping. Asthe moving coil must rotate through 'three hundred sixty degrees, it isnecessary to mount lthe top adjusting screw in the glass R. on the topof the indicator. A fine wire RI is connected to the adjusting screw andextended across the glass as shown in Fig. 5.

VBy reference to the wiring diagram ofV Fig. 1 a fixed potentialisapplied to the moving coil L and the resulting magnetic lines of forceare always in thel same direction and of the same intensity. The movingcoil L is attracted to or repelled from stationary coils HI and H2depending upon the direction and amount of current flowing through them.

In the designio/f electrically responsive instruments' such as radiodirection receivers for vehicles such as air craft, considerabledifculty is characteristically encountered in their utilization due tothe radio waves Vbeing absorbed or reradiated from objects adjacent thepick-up means. Known techniques exist for eciently determining errorsand it is an important aspect of the invention that such errors arereadily compensated for. The instrument F includes alightweightpermanent magnet S which is attached to the top Vpivot of the instrumentso that it rotates'directlyunder the scale within the casing of theinstrument. Cooperating with permanent magnet S are a plurality of smallcoils 25, 25 preferably ten in number, which are arranged around theinner periphery of the indicator so that they -will attract or repel thepermanent magnet in varying degrees, depending on the position ofthecoils in relation to the permanent nagnet, each coil being adjustable toany posilon.

To maintain uniform response from the coils wlth varying attraction fromthe two stationary coils it is necessary to vary the current across theresistor #21 and coils.#25.

The rotating contacts in switches GI and G2 are-driven by motor drivenshaft T at approximately 3,600 R. P. M., each revolution creating foursignal impulses to the receiver, and simultaneously four separatepotentials to the ends of the two stationary coils in the indicator.Three non-magnet air-damping vanes V, V are fixed to pivot L3, and serveto balance magnet S.

In operation, assuming loop BI is in line to the transmitterV tuned bythe receiver C, with loop B2 at right angles, switch GI starting atYcontact #II and rotating clockwise, the four signals applied to thereceiver C will be as follows. #II maximum, #I2, minimum, #I3intermediate, #I4 identical to #I 3. The four potentials are applied tothe two stationary coils HI and H2 in the indicator F as previouslydescribed, and will be of the following intensity, connection #4maximum, #5 minimum, #6 intermediate, #l identical to #5, as connection#4 has a higher potential above ground than connection #5, current willflow through coil H I, from connection #A to #5, #4 being positive. As#S and #l have potentials of the same value above ground, no currentwill ow through coil H2.

The current flowing in the moving coil L creates a magnetic force, thenorth pole of which is attracted to the south pole created by coil HI,and the south pole of the moving coil L is attracted to th'e north poleof coil HI, rotating the moving coil L and pointer M, which indicatesonV the scale Uthe direction of the transmitter.

Rotating the -craft and its two loops BI and B2 ninety degreesclockwise, switchGI willV apply signal voltages to the receiver C in thefollowing sequence: '#I I intermediate, #I2 identical to #I I, #I3maximum, and #I4 minimum. Therefore. an intermediate potential isapplied to #4 and a like potential to #5, a maximum potential to #E anda-minimum to #1. Subsequently no current will ilow'through coil Hi andthe current in coil H2 flowsfrom #6 to #'I, #6 being positive, rotatingthe moving coil L and pointer M ninety degrees. v Y

Rotating the loops BI and B2 clockwise anoth'er forty-ve degrees, thefour series of signals applied to theY receiver C willbe in thefollowingsequence, V#II will be 25% greater than mini,

mum and #I2 will be 50% greater than #I I, #I3 will be identical to #Iland #I4 will be identi- Cal to #I2. The Vpotentials to the ends of thestationary coils HI and H2 will be as follows: connection #4, a valuehalf waybetween the potentials applied to this contact in the twopreviously described loop positions. #5, the difference between thevoltage applied to this connection when the loops were in the rst andthe second position. #6, the same as #4, and #'I the same as #5.Therefore theV two stationary coils HI and H2 in the indicator F have alike amount of current, and #5 and #6 are positive.

The resulting magnetic elds cause the moving coil L to rotate forty-fivedegrees clockwise, the magnetic field of the moving coil being half waybetween the magnetic elds of the two stationary coils HI and H2. Anychange in the position of lthe loops, rotates the moving coil Lproportionately, the pointer M on the indicator F showing the number ofldegrees.

If it is desirable to eliminate the tone produced by the compassoperation, switch V Vmay be opened. This disconnects th'e loops BI andB2 and provides normal aural reception from the receiver C.

The radio receiver C may be of conventional design as indicated inFigure 1 and preferably comprising a superheterodyne arrangement havinga radio frequency tube 3|, a combined oscillator and modulator tube 32,an intermediate frequency amplifying tube 33, a combined detectorautomatic volume control, an audio frequency amplifying tube 34 and apower amplifying tube 35. The construction and operation of a radioreceiver of this kind vbeing well known, it will not be necessary todescribe it in detail save to explain that it connects with voltageamplifier E by conductors 31 and 43. The set includes headphones 38 forenabling the pilot to listen on the transmitting station. The receiveralso includes potentiometer 39 by means of which the volume may bemanually-adjusted as desired.

From the foregoing it will be observed that the moving coil will alwaysoperate within the fixed coils of the instrument to insure that thepointer is always directed exactly toward the station. Since theinstrument is constructed without springs it is at all times operativeto rotate through three hundred sixty degrees in eith'er directiondepending upon the course of the craft with respect to the station. Theelec trical actuation of the instrument in the described systemeliminates mechanical operations and enables a saving of weight of`one-third in comparison with socalled automatic compasses.

The provision of the essential dynamometer type of design for thepresent instrument insures long life without deterioration of originaleiiiciency and accuracy, since its direction indicating function can notdeteriorate as in the case of any types utilizing permanent magnets,Vinstead of coil L.

The instrument casing has an internal circumferential groove 44 in whichare slidable ten insulating rectangular frames 4l, 4I; ear 42 on eachframe riding in guide slot 43.

The adjustable coils are preferably adjusted when the instrument isinstalled in the craft by manually shifting the coils in the frames upor down, or radially toward or away from the permanent magnet.Additional adjustment of said coils with respect to the permanent magnetis readily accomplished if desired by sliding the coil frames around theinner periphery of the instrument. Although ten such coils and framesare shown as preferable for convenient maximum correction, it will beunderstood that a greater or lesser number may be utilized where desiredfor satisfactory compensation. Any convenient testing method may beemployed for detecting the various errors caused by the absorption orreflection of radio waves in the proximity of the pick-up means, andwhen same have been detected all of the errors may be individuallyeliminated readily by the universal mounting of the coils in theinstrument. Once the compensating positions of the coils have beenestablished the frames serve to retain them against accidentaldislocation during the subsequent utilization of the instrument. Ifdesired to compensate for error, any of the coils 25 may be turnedaround in its frame to reverse its polarity.

I claim:

1. In a :directional radio receiver having directional pickup means forreceiving signals from a distant transmitter, an electrical indicatinginstrumenthaving an indicator pointer. means responsive to said signalfor rotating said indicator pointer, a normally fixed, adjustablecompensating coil in said instrument, means maintained in fixed positionrelative to the indicator pointer for creating a magnetic field, saidadjustable coil being positionable in said instrument so as to react onsaid magnetic field for the purpose of retarding or accelerating therotation of the indicator pointer to compensate for errors caused byabsorption or reflection of radio Waves in the proximity of said pick-upmeans. means for providing a D. C. potential directly proportional tothe ysignal voltagepicked upY from said transmitter and connections fromthe latter means to said ad l'ustable coil.

2. In a radio direction nding apparatus a vertical antenna, a radioreceiver, a pair of directional loop antennae inductively coupled to theantenna and the input of the radio receiver, means for reversing theconnections of rst one loop antenna and then the other loop antenna toprovide four series of signal voltages to the receiver, such reversingmeans including a rotatable switch to provide four separate D. C. potentials proportional to the series of signal impulses and an electricalindicating instrument including an indicator pointer and meansresponsive to said potentials for rotating said pointer, means fixed tothe indicator pointer for creating a magnetic field, and normally xed,adjustable compensating coil means positioned to react on said magneticeld to retard or accelerate the rotation of the pointer.

3. In a directional radio receiver. a dynamometer type of indicatorinstrument including two fixed coils disposed respectively at an exactninety dee-ree angle. a moving coil Within said fixed coils and capableof rotation through three hundred sixty degrees an indicator pointeractuated by said moving coil, means fixed to the indicator pointer forcreating a magnetic field, and normally fixed. adjustable compensatingcoil means positioned to react on said magnetic field to retard oraccelerate the rotation of the pointer.

4. In a directional radio receiver, an electrical indicating instrumentincludingr means for creating a magnetic field capable of rotationthrough three hundred sixty degrees and having a fixed intensity andpolarity, means for creating two fixed magnetic fields, one said fieldbeing disposed exactly ninety degrees with respect to the other, saidfields being capable of varying in intensity and polarity, said rstmeans rotating within said fixed means an indicator pointer actuated bysaid first means, means fixed to the indicator pointer for creating amagnetic field, and normally fixed, adjustable compensating coil meanspositioned to react on said magnetic field to retard or accelerate therotation of the pointer.

5. In a directional radio receiver having pickup means. an electricalindicating instrument including an indicator pointer and having normallyfixed, adjustable compensating coil means, means fixed to the indicatorpointer for creating a magnetic field, said adjustable coil means beingpositioned to react on said magnetic field for the purpose of retardi'ngor accelerating the rotation of the pointer to compensate for errorscaused b-y absorption or reflection of radio waves in the proximity ofthe pick-up means.

6. In a directional radio receiver having pickup means and an electricalindicating instrument having an indicator pointer, a normally fixed,adjustable compensating coil, and means maintained in fixed positionrelative to the indicator pointer for creating a magnetic field, saidadjustable coil being positionable to react on said magnetic field forthe purpose of retarding oraccelerating the rotation of the indicatorpointer to compensate for errors caused by absorption or reflection ofradio Waves in the proximity of said pickup means.

' 7. In a radio direction finding apparatus a Vertical antenna, a radioreceiver, a pair of directional loop antennae inductively coupled to theantenna and the input of the radio receiver,

-means for reversing the connections of first one loop antenna and thenthe other loop antenna to provide four series of signal voltages to thereceiver, such reversing means including a rotatable switch to providefour separate D. C. potentials proportional to the series of signalimpulses, four capacitors alternately charged by the four separate D. C.potentials, two stationary coils in an indicator and connections fromsaid coils to the four capacitors.

8.- In a directional radio receiver having pickup means, an electricalindicating instrument including an indicator pointer and having normallyfixed, adjustable compensating coil means, means fixed to vthe indicatorpointer for creating a magnetic field, said adjustable coil means beingpositioned to react on said magnetic eld for the purpose of retarding oraccelerating the rotation of the pointer to compensate for errors causedby absorption or reflection of radio Waves in the proximity of thepick-up means, and a retaining element for said coil means movablearound said pointer.

9. In a directional radio receiver having pickup means and an electricalindicating instrument having an indicator pointer, a normally fixed,adjustable compensating coil, means maintained in fixed positionrelative to the indicator pointer for creating a magnetic field,A aframe element frictionally engaging said coil and being movable in theinstrumentwith respect to said pointer, said adjustable coil beingmovable in said frame upon manual adjustment for altering intensity orits polarity to react on said magnetic eld for the purpose of retardingor accelerating the rotation of the indicator pointer to compensate forerrors caused by absorption or reflection of radio Waves in theproximity of said pick-up means.

l0. In a directional radio receiver having pickupV means and anelectrical indicating instrument having-an indicator pointer, aplurality of normally fixed, adjustable compensating coils, and meansmaintained in fixed position relative to the indicator pointer forcreating a magnetic eld, said adjustable coils being positionable to.

react on said magnetic field for the purpose of retarding oraccelerating the rotation of the indicator pointer to compensate forerrors caused by absorption or reflection of radio Waves in theproximity of said pick-up means.

11. In a directional radio receiver having Ypiola-up means and anelectrical indicating instrument having an indicator pointer, aplurality of adjustable coils, and means maintained in fixed positionrelative to the indicator pointer vfor rcreating a magnetic eld, saidadjustable coils being positionable radially, longitudinallyy andcircumferentially with respect to said pointer so las to react on saidmagnetic field for the purpose of retarding or accelerating the rotationof the indicator pointer to compensate for errors l caused by absorptionor reflection of radio waves

